Ferromagnetic material of the formula bafe3o5f and its preparation



United States Patent FERROMAGNETICMATERIAL OF THE FORMULA BaFe O F ANDITS PREPARATION Lothar' Heinrich Brixner, Wilmington, Del'., assignor toE. I. du' Pont de Nemours and Company, Wilmington, Deh, a corporation ofDelaware No Drawing. Application July 19, 1957 Serial No. 672,883

5 Claims. (Cl. 23-50) This invention relates to a new ferromagneticcomposition represented by the formula BaFe O F.

Ferromagnetic materials might broadly be classified into two groups:those with low coercivities, and those with high coercivities. Materialsof the former type are useful in transformers, magnetic amplifiers,memory cores, and microwave devices, and include such well-knownsubstances as the Permalloys, silicon irons, and certain ferritestheferrites being materials having the general formula MO-Fe' O- where M isa divalent metal. The ferromagnetic materials with high coercivitiesinclude the permanent magnetic materials, such as BaO-6Fe O andmanganese bismuthide (MnBi). It follows, obviously, that ferromagneticmaterials of high coercivity provide better permanent magnetcharacteristics than those with low coercivity. The ferromagneticmaterial described in this invention possesses an exceptionally highintrinsic coercive force, and it is represented by the chemical formulaBaFe O F. It has a crystalline structure, but this structure is unlikethat of such known ferromagnetic materials as the ferrites and BaO-6Fe Owhich is of the magneto plumbite type. X-ray analysis indicates that thecomposition contains none of the uncombined starting materials, and thatit is different from the pattern of BaFeO F which might be considered tobe an intermediate product in the preparation of my new crystallinematerial.

The ferromagnetic material of my invention may be prepared by startingwith a mixture of BaCO BaF and Fe O in a molecular ratio of 1:1:1; i.e.,in amounts required to form 2 mols BaFeO F with the evolution of 1 molof CO This mixture is heated at a temperature of approximately 1000 C.,and then cooled to room temperature and pulverized. The pulverizedproduct is mixed with powdered Fe O in a stoichiometric quantity basedon the formation of BaFe O P. This mixture is then fired and cooled. Theresulting crystalline material is also pulverized, and then compactedinto a unitary mass of desired shape by pressing or extruding. This massis subjected to firing to produce the ferromagnetic material of thisinvention.

For a clearer understanding of the invention, the following specificexample is given. This example is intended to be merely illustrative ofthe invention and not in limitation thereof. Unless otherwise specifiedall parts are by weight.

Example According to the equation BaCO +BaF +Fe O ZBaFeO F-l-COstoichiometric amounts of reactants were ground together in an agateball mill to a fineness of 200 mesh. These amounts by weight were 5.454gms. of BaCO 4.8468 gms. of BaF and 4.4129 gms. of Fe O After thoroughmixing, the powder was placed in a platinum crucible and heated in airat a temperature of approximately 1000 C. for 4 hours. The crucible wastaken from the furnace, allowed to cool to room temperature, and thereaction 2,893,830 Patented July- 7, 1959 "ice was ground with 1 .9226gms. ofthe fired material in an agate ball mill to a fineness: of -200mesh. The mixture was then transferred toxa platinum crucible and washeated in air to a temperature of approximately 1200 C. and held. atthis temperature for two hours. The crucible was removed from: thefurnace, allowed to cool to room: temperature, and the contentspulverized to a -200 mesh by grindin'g. in the agate ball mill. Theground material was shaped intorapellet /2 inch in diameter at apressure of 190,000 p.s.i. This pellet was subjected to an additionalfiring at approximately 1200 C. for one hour. The material. thusproduced was a dark brown-black compactpellet which was useful as amag.- net. When examined. by X-ray analysis, there was no indication ofthe uncombined components which were present prior to the last firing.The magnetic properties as determined with. a pressed cylindricalwspecimen of density 3.96 gm./ cc. were as. follows:

B saturationma'gneti'zation (4rd,) 970 gauss.

The above values of the magnetic properties were obtained with aSanford-Bennett high field permeameter from the Rubicon Company. Acylindrical sample /2" diameter and about 1% long) was butted betweenthe pole pieces of the permeameter and subjected to the standardoperating procedure for obtaining the demagnetizing curve.

Alternatively, other decomposable compounds like Fe(NO and Ba(NO mightbe used as alternative starting compounds. Commercially availableproducts of the highest purity are preferred as starting materials.Although the example specifies firing temperatures of 1000 C. for thefirst firing and 1200 C. for the subsequent two firings, both of thesetemperatures may vary as much as C. without effecting any substantialchange in the results obtained. Similarly, the times of heating whichhave been given in the example as four hours for the first heating, twohours for the second, and one hour for the third, may vary as much as,say, :1 hour for the first and second heating and 1 /2 hour for thethird firings, the shorter times being used with the highertemperatures.

It will be seen from the above data on my novel magnetic crystallinematerial, particularly the values which were obtained for remanentmagnetization and for intrinsic coercivity, that this material isvaluable as a permanent magnet and would be useful in the manyapplications known for such a material. Among these would be rotatingmechanical couplings, television focusing yokes, refrigerator andcabinet door latches, motors, and generators.

Since it is obvious that many changes and modifications can be made inthe above-described details without departing from the spirit and scopeof the invention, it is to be understood that the invention is not to belimited to said details except as set forth in the appended claims.

I claim:

1. As a composition of matter, a ferromagnetic material of the chemicalformula BaFe O F.

2. As a composition of matter, a ferromagnetic material of the chemicalformula BaFe O F, with an intrinsic coercivity of about 3700 oersteds, aremanent magnetization of about 750 gauss, a maximum energy product ofabout 135,790 gauss-oersteds and a specific resistance of about ohm-cm.

3. A process for producing a ferromagnetic material which comprisesheating at a temperature of about 900 C.-1100 C. for about 3-5 hours apowdered mixture comprising (1) BaF (2) an inorganic iron compoundselected from the group consisting of Fe O and Fe(NO and (3) aninorganic barium compound selected from the group consisting of BaCO andBa(NO said barium and iron compounds being present in a molecular ratioof 1:1:1, cooling the product thus obtained, grinding the product to apowder, and incorporating with said powder, powdered Fe O in astoichiometric amount according to the equation:

heating the latter mixture at a temperature of about 1100 C.1300 C. forabout 1 hour-3 hours, cooling the product thus obtained, grinding theproduct to a powder, compacting the powder into a unitary mass andheating said mass at a temperature of about 1100 C.- 1300 C. for aboutV2 hour-1V2 hours to convert said latter mixture to ferromagneticmaterial of the formula BaFe O F and recovering said BaFe 'O F material.

4. A process for producing a ferromagnetic material which comprisesheating at a temperature of about 900 C.-1100 C. for about 3-5 hours apowdered mixture comprising BaF R2 0 and BaCO said barium and ironcompounds being present in a molecular ratio of 1:1:1, cooling theproduct thus obtained, grinding the product to a powder, andincorporating with said powder, powdered Fe O in a stoichiometric amountaccording to the equation:

heating the latter mixture at a temperature of about 1100 C.-1300 C. forabout 1 hour3 hours, cooling the product thus obtained, grinding theproduct to a powder, compacting the powder into a unitary mass andheating said mass at a temperature of about 1100 C.1300 C. for about /2hour-1V2 hours to convert said latter mixture to ferromagnetic materialof the formula BaFe O F and recovering said BaFe O F material.

5. A process for producing a ferromagnetic material which comprisesheating at a temperature of about 1000 C. for about 4 hours a powderedmixture comprising BaF Fe O and BaCO said barium and iron compoundsbeing present in a molecular ratio of 1:1: 1, cooling the product thusobtained, grinding the product to a powder, and incorporating with saidpowder, powdered Fe O in a stoichiometric amount according to theequation:

heating the latter mixture at a temperature of about 1200 C. for abouttwo hours, cooling the product thus obtained, grinding the product to apowder, compacting formula BaFe O F and recovering said BaFe O F material.

No references cited.

1. AS A COMPOSITION OF MATTER, A FERROMAGNETIC MATERIAL OF THE CHEMICALFORMULA BAFE3O5F.